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1. Field of Invention
This invention pertains to utilization of magnetic tape for information storage, and particular to magnetic tape having a servo or tracking signal buried therein.
2. Related Art and Other Considerations
Magnetic tape can have information recorded thereon by creating magnetic flux transitions on the magnetic tape media. The flux transitions are typically created by the application of a signal to a recording element or "head". The flux transitions are recorded by the head along a "track" of the tape media.
In order, e.g., for information to be read from the tape, servoing or tracking techniques are conventionally provided to enable the head to follow accurately or be aligned with a track of recorded information. In some servoing techniques, a servo signal is recorded while user data is being recorded on the tape media. The servo signal is recorded at a frequency other than the frequency of user data to be distinguishable therefrom, and may be read by either the same head which reads or records user data or a head dedicated for recovery of the servo signal.
In another servoing technique, a servo signal is pre-recorded on the tape by the tape manufacturer. This pre-recorded servo signal is permanently provided on the tape, i.e., is not erasable by user data, and is sometimes referred to as a deep or buried servo signal. The buried servo signal is recorded at a frequency which is readily distinguishable from that of user data.
It has been previously proposed that a buried servo signal be modulated to provide an indication of sectorization of the tape media. For example, where the user data on the media is to be segmented into uniformly sized sectors or frames of information (e.g., a "hard sectored" media), the delineation of one frame from another frame can be provided by modulation of the servo signal.
In order to determine the current position of hard sectored media, an apparatus handling the media (e.g., a tape drive) must fully rewind the media and keep track of the number of frames encountered (based on servo signal modulation) as the tape is read. This counting of frames relative to an end of the media is error prone and time consuming, and moreover provides no way of providing an indication of tape location in a mid-tape load (e.g. when a cartridge of non- rewound tape is loaded into a drive).
What is needed therefore, and an object of the present invention, is modulation of buried servo information to provide more than relative alignment of a head and a track. A particular advantage of the present invention is modulation of buried servo information to provide an indication of head position relative to tape media.